Method of nitriding



May 5, 1936- L. B. I INDEMUTH 2,039,487

METHOD OF NITRIDING v Filed May 28, 1929 M 5y l ATTORNEY YPatented May 5,. 1936 -UNITED STATES m01) 0F NITRIDING Lewis B. Hndemuth, Albany, N. Y., assignor, by mesne alignments, to The Nitralloy Corporation, a corporation of Delaware y Application May 28, 1929, Serial No. 366,154

ZCIaims.

My invention relates to a method for surface hardening materials by the nitriding process. It also contemplates a novel and improved method for heating the materials to be nitrlded and 5 maintaining the materials at the proper temperature during the nitriding treatment. VHeretofore it has been the practice to heat the materials to be treated and then pas cold ammonia gas into the nitriding chamber. In my 10 method this procedure is substantially reversed.

- and a uniformly hardened product is assured.

My invention relates particularly to the hard- ,u ening by nitriding of hollow objects, such as cylinders and cylinder liners foi internal combustionengines. In hardening cylinders and cylinder liners, it is essential that the internal grolmd surfaces be uniformly hardened. 'lhe external u surl'acesaredeslrablynothardenedandifthey are exposedduringthenitrlding operationand become hardened this results in a. needless consumption ammonia or other nitriding agent employed. It has been customary in hardening ,o mcharticlestoprotectthesurtacesnotdesired to be hardened by asuitable coating or covering. which usually must be removed after the nitrlding operation, thus 'involving additional manipulation and expense.

"g5 ly invention therefore includes the hereincomparatively high velocity through the piping system and nitriding chamber.

An ammonia inlet pipe, l, equipped with a valve, l, is provided on the intake side of the fan, and. a valved outlet, 9, is also provided for the Spent gas.

Within the .piping system, 4, and preferably Aon the discharge side of the fan, a plurality of electrically heated grids, 23, are provided for heating the ammonia gas as it is circulated over and through them. These grids are/of pure nickel or of a nickel 4alloy adapted to act also as a catalyzer for producing nascent nitrogen.

Referring now more particularly to Fig. 2, I have here illustrated a type of furnace in .which the direction of iiow of gas through the nitriding chamber may be reversed without reversing the direction of rotation of the motor. I accomplish this by means of the piping system illustrated and by providing therein adjustable dampers or valves for controlling the direction of gas flow. Here the piping system, I, is substantially identical with the system shown in Fig. 1, but an additional cross pipe, Il), parallel to the nitriding chamber, is provided as shown, and the blower, Il, driven by motor, I2, is located in the short pipe, I3, connecting the center of pipe, Il, with the Piping system, I. A

Electrical ristance heating elements, I5 and I6, similar to those above described, are provided in the pipes, 4. Two are here provided because the direction of the flow of gas through the nitriding chamber is reversible and it is preferable to heat the gas just before it enters the chamber.

At each end oi pipe, I3, I provide a. butterfly valve, Il and Il, respectively, which may be manipulated to control the direction of flow of gas through the nitriding chamber. When the valves are set in the position shown by the solid lines 40 inllg.2thegaswillilowinonedirectionthrough the nitriding chamber. When the valves are in the position indicated by the dotted lines in Fig. Zthedirectionoftheilowofgasthroughthe chamber will be reversed.

As in the species shown in Fig. 1, I provide an ammonia inlet as shown at IQ, and a valve, 2l, l for controlling the same. In this typeoi' furnace two valved outlets, 2l and 22, respectively, may be provided for the release of the spent gas.

From the foregoing it will be apparent that the ammonia gas in passing over and about the electrically heated grids will absorb heat there- Irom,carrythistothenitridingchamberand theretransmitittothe objects or materials to be nitrided. In other words, instead of following the usual procedure of heating the objects to be nitrlded and then introducing cold ammonia gas into the nitriding chamber, this procedure is, in a wayreversed. By using a preheated ammonia gas in a closed circuit a flow thereof through the nitriding chamber can be main'- tained at comparatively high velocity, thus eliminating all pockets of stagnant gas which occur in furnaces of the present type and which cause lack of uniformity in the nitrided product.

It will also be apparent that my general arrangement of the heating elements and a fan for circulating the ammonia gas and heating it prior ment of cylinders for internal combustion engines A and the like. As above stated it is desirable to nitride harden only theinterior of the cylinders.

and this may be done by substituting the cylinder itself, or a plurality thereof, suitably arranged toform a part of the conduit system, for the nitriding chamber, l. In other words, the cylinder itself would form a portion of the passageway through which the ammonia gas passes. y

While I have described my invention in its preferred embodiment it is to be understood that the words whichrI have used are words of description rather than of limitation and that the drawing is merely illustrative. Hence changes,

within the purview of the appended claims, may

article.

be made without departing from the true scope and spirit of my invention.

What I claim is- 1. In the art of nitriding localized portions of articles made of alloys of steel or cast iron, the steps which comprise disposing the localized portion of said article that is to be nitrided so that it forms a portion of a Wall of a nitriding chamber, imparting violent motion to a nitrogen-yielding gas in reactive relation to said localized portion by introducing said gas into said chamber under elevated pressure, causing said gas to circulate rapidly through said chamber, repeatedly returning said gas to said chamber in a substantially closed cycle, and supplying heat to said gas in the course of its cyclic ow at a point outside of and in substantially heat isolated relation to said chamber.

2. In the art of nitriding, articles made of alloys of steel or Ycast iron, the steps which com'- prise disposing a tubular article having interior surfaces to be nitrided, in a conduit system so that it forms a part of said system, causing a nitrogen-yielding gas to pass through said ccnduit system into contact with said surfaces. and repeatedly returning said gas to said chamber in -a substantially closed cycle, supplying heat to said gas in the course of its cyclic ow at a point outside'of and remote from said tubular LEWIS B. LINDEMUTH. 

